Fair Value Measurements (Narrative) (Details) - Diesel swap gal in Millions	12 Months Ended
Dec. 31, 2016 $ / gal gal
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount (in gallons) \| gal	7.0
Derivative, notional amount (in dollars per gallon)	2.56
Average forward price (in dollars per gallon)	2.73

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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